JPH10190115A - Multi-beam writing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce uneven concentration in a picture due to the characteristic variation between two semiconductor lasers, by controlling the APC of the semiconductor lasers with one reference voltage. SOLUTION: A multi-beam writing device is provided with a plurality of laser light sources 2 and 3, and is constituted to optically perform writing by simultaneously scanning a photosensitive drum with a plurality of laser beams emitted from the laser light sources 2 and 3 in accordance with picture signals. The writing device is provided with photodetectors 4 which detect part of the laser beams emitted from the laser light sources, and reference voltage generating circuits which generate reference voltages V3 and V4 independently adjusted in advance at every laser source. The device controls the light quantity of each laser light source to a desired value, by comparing the output signals of the photodetectors with the reference voltages of their corresponding reference voltage generating circuits.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing apparatus used for a laser beam printer, a digital copying machine, etc., and more particularly to a multi-beam writing apparatus for performing optical writing using a plurality of light beams. .

[0002]

2. Description of the Related Art In recent years, a multi-beam writing system for performing optical writing by using a plurality of laser light sources and simultaneously scanning laser beams of the respective laser light sources on a photosensitive member has been studied. Such a multi-beam writing method,
By irradiating the photosensitive member with a plurality of scanning lines simultaneously, not only high-speed printing is possible, but also the rotational speed of the rotating polygon mirror can be reduced, so that the speed of the scanner motor can be easily controlled. is there.

FIG. 2 shows an example of such a multi-beam writing system. In FIG. 2, reference numeral 1 denotes a semiconductor laser array having two semiconductor lasers 2 and 3, and 4 denotes a photodetector such as a photodiode for detecting the laser beams of the semiconductor lasers 2 and 3. The semiconductor laser array 1 and the photodetector 4 are integrated as a laser chip as shown in FIG. 3, and the semiconductor laser array 1 and the photodetector 4 are respectively arranged on the base 5 in close proximity.

A semiconductor laser array 1 comprises two semiconductor lasers 2 and 3 formed at a predetermined interval.
Back beams 2b, 3b emitted from semiconductor lasers 2, 3
Are respectively detected by the photodetector 4. Laser drive circuit 11,
Numeral 12 is a circuit for driving the semiconductor lasers 2 and 3 according to the image signals supplied from the MPU 13, respectively. The laser beams 2a and 3a emitted from the semiconductor lasers 2 and 3 are linearly formed by a rotary polygon mirror (not shown). , And irradiates a photosensitive drum (not shown) to form a latent image and perform optical writing.

The amplifier 6, the sample and hold circuits 7, 8, and the comparators 9, 10 are circuits for controlling the light amounts of the semiconductor lasers 2, 3 to be constant. Semiconductor lasers 2, 3
Is detected by the control of the MPU 13 during a blanking period (non-image area) in which optical writing is not performed. Specifically, the MPU 13 controls the laser drive circuit 11 in the non-image area.
And 12 are sequentially controlled to cause the semiconductor lasers 2 and 3 to emit light in time series. When the semiconductor laser 2 emits light, its back beam 2b is detected by the photodetector 4 and converted into an electric signal. The output signal of the photodetector 4 is amplified by the amplifier 6 and then output to the sample and hold circuit 7.

The comparator 9 compares the output voltage V1 of the sample and hold circuit 7 with a reference voltage Vs adjusted by a variable resistor in advance, and outputs a control signal corresponding to the difference to the laser drive circuit 11. The laser drive circuit 11 increases or decreases the drive current of the semiconductor laser 2 according to the control signal, and performs control so that the light amount of the semiconductor laser 2 becomes the target light amount given as the reference voltage. That is, the sample hold circuit 7
If the output voltage V1 is higher than the reference voltage Vs, the drive current of the semiconductor laser 2 is reduced, and if the output voltage V1 is lower than the reference voltage Vs, the drive current of the semiconductor laser 2 is increased to reduce the light amount of the semiconductor laser 2. Control to constant.

When the semiconductor laser 3 emits light, the back beam 3b is similarly detected by the photodetector 4, converted into an electric signal, and output to the amplifier 6. The output signal of the amplifier is similarly output to the sample and hold circuit 8. The comparator 10 compares the output voltage V2 of the sample and hold circuit 8 with the reference voltage Vs, and outputs a control signal corresponding to the difference to the laser drive circuit 12. Similarly, the laser drive circuit 12 increases or decreases the drive current of the semiconductor laser 3 according to the control signal, and performs control so that the light amount of the semiconductor laser 3 becomes constant.

In this manner, in the non-image area, each of the semiconductor lasers 2 and 3 is turned on in a time-division manner to perform APC control (Au
tomatic Power Control). On the other hand, in the image area, the sample and hold circuits 7 and 8 hold the light quantity signals of the semiconductor lasers 2 and 3 respectively, and the laser drive circuits 11 and 12 use the held light quantity signals and respectively use the semiconductor lasers 2 and 3. Is controlled to a target light amount. As described above, in the related art, the light amounts of the two semiconductor lasers 2 and 3 are controlled to be constant regardless of a change in ambient temperature.

[0009]

In the prior art, as described above, APC control of each semiconductor laser is performed using one reference voltage Vs. Incidentally, in order to determine the reference voltage Vs, the reference voltage Vs is adjusted according to the characteristics of one of the two semiconductor lasers, and the APC control of the two semiconductor lasers is performed with the adjusted reference voltage. Is going. Therefore, another semiconductor laser performs APC control with a reference voltage adjusted according to the characteristics of the other semiconductor laser.
However, in such an adjustment method, since the characteristics of the two semiconductor lasers are different, if APC control of the two semiconductor lasers is performed using a reference voltage adjusted according to the characteristics of one of the semiconductor lasers, The image density varies due to the difference in characteristics.

For example, since the emission wavelengths of the two semiconductor lasers are not always the same, when optical writing is performed on a photosensitive drum having sensitivity characteristics with respect to the emission wavelength, the charge amount of the latent image formed on the photosensitive drum surface is reduced. A difference occurs, and a difference in image density appears at an interval between semiconductor lasers in a printed image, resulting in uneven density. Further, since the spread of the laser light of the semiconductor laser is different when the laser light is emitted, if the laser light is narrowed down by the optical system, the beam spot diameter varies due to the difference of the spread of the laser light of each semiconductor laser. Therefore, also in such a case, there is a problem that density unevenness occurs in the printed image due to the variation of the beam spot diameter.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a multi-beam writing apparatus capable of obtaining a high-quality image without density unevenness regardless of the inherent characteristics of a laser light source. It is.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plurality of laser light sources, each of which is driven in accordance with an image signal, and a plurality of laser lights emitted from each of the laser light sources are used as an image carrier. In a multi-beam writing device that performs optical writing on an image carrier by simultaneously scanning on the
A detection element for detecting a part of the laser light emitted from each of the laser light sources, and a reference voltage which is provided corresponding to each of the laser light sources and is adjusted independently for each of the laser light sources. A reference voltage generation circuit, and controlling the light amount of each laser light source to a desired light amount by comparing the output signal of the detection element and the reference voltage of the corresponding reference voltage generation circuit for each laser light source. This is achieved by a multi-beam writing device characterized by the following.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of the multi-beam writing apparatus according to the present invention. In FIG. 1, the same parts as those of the conventional apparatus of FIG. 2 are denoted by the same reference numerals. In FIG. 1, reference numeral 1 denotes a semiconductor laser array having two semiconductor lasers 2 and 3;
Is a photodetector such as a photodiode. The semiconductor laser array 1 and the photodetector 4 are integrated as shown in FIG. That is, as shown in FIG. 3, a semiconductor laser array 1 is fixed on a base 5 and a photodetector 4
Is fixed. The back beams 2b and 3b of the semiconductor lasers 2 and 3 are respectively detected by the photodetector 4, and APC control of the semiconductor lasers 2 and 3 is performed using an output signal of the photodetector 4 as described later in detail.

The amplifier 6, the sample and hold circuits 7, 8, the comparators 9, 10, and the laser driving circuits 11, 12 are all the same as those in FIG. The amplifier 6 amplifies the output signal of the photodetector 4, the sample and hold circuits 7 and 8 sample and hold the light intensity signals of the semiconductor lasers 2 and 3 amplified by the amplifier 6, respectively, and the comparators 9 and 10 sample and hold, respectively. The output signals of the circuits 7 and 8 are compared with a predetermined reference voltage, and a control signal corresponding to the difference is output to the laser drive circuits 11 and 12.

The laser drive circuits 11 and 12 control the drive current according to the control signals so that the light amounts of the semiconductor lasers 2 and 3 become the target light amounts. The MPU 13 is a processor circuit for controlling the entire apparatus. In the non-image area, the MPU 13 turns on the two semiconductor lasers 2 and 3 in a time-division manner and performs APC control of each semiconductor laser. On the other hand, in the image area, image data is supplied to the laser drive circuits 11 and 12, and optical writing is performed on a photosensitive drum (not shown). In the image area, the light intensity signals of the semiconductor lasers 2 and 3 are held in the sample hold circuits 7 and 8, and APC control is performed using the held light intensity signals.

In this embodiment, the semiconductor lasers 2 and
3 are provided with reference voltage generating circuits for generating reference voltages. The reference voltage generation circuit of the semiconductor laser 2
The variable resistor 15, 16 comprises a series circuit of variable resistors 15, 16 and a switch element 18 such as a MOS transistor, and regulates a previously stabilized power supply voltage V by the variable resistors 15, 16. Then, the adjusted reference voltage V3 is applied to the semiconductor laser 2
Is input to the comparator 9 as a reference voltage for the APC control. The reference voltage generating circuit of the semiconductor laser 3 is composed of a series circuit of variable resistors 15 and 17 and a switch element 19 such as a MOS transistor. The power supply voltage V is adjusted by the variable resistor 17 so that a desired reference voltage is obtained. V4 has been obtained. The adjusted reference voltage V4 is input to the comparator 10 as a target light amount of the semiconductor laser 3.

Here, the reference voltages V3 and V4 are independently adjusted in advance according to the individual characteristics of the semiconductor lasers 2 and 3 when adjusting the apparatus. Specifically, first,
When adjusting the light quantity of the semiconductor laser 2, the switch element 18 is turned on under the control of the MPU 13 and the switch element 1 is turned on.
9 is turned off. In this state, the laser drive circuit 11 is activated by the control of the MPU 13, and the semiconductor laser 2 is turned on. At this time, the variable resistors 15 and 16 are adjusted so that the light amount of the semiconductor laser 2 becomes a desired light amount. That is, when the semiconductor laser 2 is turned on, the APC control is activated, and the light quantity signal of the semiconductor laser 2 is fed back to the comparator 9. At this time, the variable resistors 15, 1
6, the reference voltage V3 is adjusted so that the light amount of the semiconductor laser 2 becomes a desired light amount.

When the adjustment of the reference voltage V3 is completed, the switch element 18 is turned off and the switch element 19 is turned on. In this state, the laser drive circuit 12 is activated, and the semiconductor laser 3 is turned on. At this time, by adjusting the variable resistor 17 in the same manner, the reference voltage V4 is adjusted so that the light amount of the semiconductor laser 3 becomes a desired light amount. As described above, in the present embodiment, the reference voltages of the semiconductor lasers 2 and 3 are independently adjusted according to the characteristics of each of the semiconductor lasers 2 and 3.

Next, a specific operation of the multi-beam writing apparatus according to the present embodiment will be described. First, the MPU 13 operates the laser drive circuit 1 in a non-image area where optical writing is not performed.
By controlling the semiconductor lasers 1 and 12, the semiconductor lasers 2 and 3 are turned on in a time-division manner for a predetermined time. Further, in synchronization with this, the switch elements 18 and 19 are turned on in a time sharing manner. When the semiconductor laser 2 is turned on, its back beam is detected by the photodetector 4,
The output signal of the photodetector 4 is input to the comparator 9 via the amplifier 6 and the sample hold circuit 7.

On the other hand, at this time, the switching element 18 is on (the switching element 19 is off), and the reference voltage V3 adjusted according to the characteristics of the semiconductor laser 2 as described above.
Is input to the comparator 9. The comparator 9 compares the output signal of the sample hold circuit 7 with the reference voltage V3 and outputs a control signal according to the difference, and the laser drive circuit 11 controls the drive current of the semiconductor laser 2 according to the control signal. The APC control operates in this manner, and the light intensity signal of the semiconductor laser 2 at this time is held by the sample hold circuit 7.

When the semiconductor laser 3 is turned on, a back beam is similarly detected by the photodetector 4, and the detected light amount signal is input to the comparator 10 via the amplifier 6 and the sample hold circuit 8. On the other hand, at this time, the switch element 19 is on (the switch element 18 is off) under the control of the MPU 13, and the reference voltage V 4 adjusted according to the characteristics of the semiconductor laser 3 is input to the comparator 10. The comparator 10 outputs a control signal according to the difference, and the laser drive circuit 12 controls the drive current of the semiconductor laser 3 according to the control signal. APC control works in this way,
The light amount signal at this time is similarly held in the sample hold circuit 8.

In the image area, the MPU 13 supplies image data to the laser drive currents 11 and 12, respectively. The MPU 13 turns on the switch elements 18 and 19 in synchronization with the image data. As a result, the semiconductor lasers 2 and 3 are driven in accordance with the image data, respectively, and the laser beams modulated in accordance with the image data from the semiconductor lasers 2 and 3 are linearly moved by the deflectors (not shown) to the photosensitive drums. (Not shown).

In this case, the light quantity signal is held in the sample and hold circuits 7 and 8 as described above, while the switch elements 18 and 19 are turned on in synchronization with the image data. Each switch element 1
Reference voltages V3, V supplied when 8, 19 are turned on
4, the APC control is activated, and the light amounts of the semiconductor lasers 2 and 3 are respectively controlled to target light amounts. In this way, the MPU 13 supplies the image data to the laser drive circuits 11 and 12 sequentially, scans the photosensitive drum with laser light to perform optical writing, and forms a one-page latent image on the photosensitive drum. Thereafter, printing is performed by developing the latent image using toner, transferring the toner image to a recording sheet, and fixing the transferred toner image.

[0024]

As described above, according to the present invention, the reference voltage is independently adjusted for each laser light source in accordance with the characteristics of the laser light source. Variations in the spread of light and the like can be absorbed by adjusting the reference voltage according to the characteristics of each laser light source. Therefore, it is possible to prevent the density unevenness of the image caused by the variation in the characteristics of the laser light source, and it is possible to obtain a high-quality image without the density unevenness regardless of the inherent characteristics of the laser light source. In addition, since the reference voltage of each laser light source can be adjusted individually, by adjusting according to the sensitivity of the photosensitive drum when replacing the photosensitive drum,
A constant image quality can be obtained even with respect to variations in the sensitivity of the photosensitive drum.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a multi-beam writing device according to the present invention.

FIG. 2 is a circuit diagram showing a conventional multi-beam writing device.

FIG. 3 is a perspective view showing a configuration of a semiconductor laser and a photodetector of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser array 2, 3 Semiconductor laser 4 Photodetector 6 Amplifier 7, 8 Sample hold circuit 9, 10 Comparator 11, 12 Laser drive circuit 13 MPU 15-17 Variable resistor 18-19 Switch element

Claims (1)

[Claims] An image carrier is provided by driving a plurality of laser light sources according to an image signal and simultaneously scanning a plurality of laser beams emitted from each laser light source on an image carrier. In a multi-beam writing apparatus for performing optical writing on a body, a detecting element for detecting a part of laser light emitted from each of the laser light sources and a laser light source provided for each of the laser light sources are provided. A reference voltage generation circuit that generates a reference voltage independently adjusted in advance for each laser light source, by comparing the output signal of the detection element for each laser light source and the reference voltage of the corresponding reference voltage generation circuit, A multi-beam writing device wherein the light amount of each laser light source is controlled to a desired light amount.